1. Technical Field
The present invention relates to a radar device which uses a radio frequency signal.
2. Description of the Related Art
In recent years, techniques for determining a position with high accuracy have come to attract attention in such fields as security, logistics, and ITS (Intelligent Transport Systems). And radar technologies using a high-frequency radio signal have been developed as position determining methods. An FMCW (frequency-modulated continuous wave) radar technology, a pulse radar technology, etc. are known as radar technologies of the above kind.
In FMCW radars, a distance to a reflective object is determined by transmitting a transmission signal while varying the frequency of a carrier signal and performing a frequency analysis on a reception signal that is reflected from the reflective object and received by the radar. A pulse radar technique is a technique in which a distance to a reflective object is measured by transmitting a pulse signal having a short duration as a transmission signal and detecting a time to reception, by the radar, of the transmission signal reflected by the reflective object.
Pulse radars will be described below. In pulse radars, a pulse signal transmitted from a radar is reflected by various objects existing in the space and hence reflection waves coming from various directions and having various delay times are received by the radar as incoming waves. This kind of environment is called a multipath environment. In a multipath environment, if two incoming wave signals have delay times that are shorter than a pulse width, reception pulses of these incoming wave signals overlap with each other and hence it is difficult to separate the two incoming wave signals.
As in understood from the above description, the separation resolution of two incoming wave signals is determined by the pulse width of a pulse signal. Therefore, as the pulse width is shortened, the separation resolution increases and the degree of degradation due to a multipath environment can be lowered. Thus, to realize a high separation resolution for high-accuracy position determination, it is required to shorten the pulse width.
To shorten the pulse width, it is necessary to deal with wideband signals. This necessitates wideband analog circuits or high-speed digital circuits in a signal processing section of each of a transmitter and a receiver. In particular, it is necessary to increase the processing speed of an AD conversion circuit which converts an analog signal into a digital signal or a DA conversion circuit which performs opposite processing, that is, converts a digital signal into an analog signal.
In sampling for converting an analog signal into a digital signal, to satisfy the sampling theorem, it is necessary to sample a sampling subject signal with a bandwidth that is two times or more as broad as its bandwidth. Therefore, to narrow the pulse width for the purpose of increasing the accuracy of a radar, it is necessary to perform sampling at shorter intervals accordingly.